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991.
基于单根10 m大模场面积保偏光子晶体光纤, 搭建了带有色散图的放大自相似振荡器; 通过仔细调节腔内色散量的大小以及位于色散补偿端的端镜前的狭缝位置和大小, 实现了稳定的锁模运转, 获得了抛物线形脉冲输出. 输出脉冲的重复频率为8.6 MHz, 脉冲宽度为6.2 ps, 光谱宽度为3.84 nm, 平均功率820 mW, 对应单脉冲能量95 nJ. 这是第一次在自相似振荡器中直接获得重复频率在10 MHz 以下的脉冲输出, 95 nJ也是目前自相似振荡器直接输出的最高脉冲能量. 通过数值模拟证实了在第一个光栅的零级反射处和狭缝滤波后可以分别实现抛物线型脉冲和高斯脉冲的两种锁模脉冲输出. 相似文献
992.
PET image reconstruction with a system matrix containing point spread function derived from single photon incidence response
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A point spread function(PSF)for the blurring component in positron emission tomography(PET)is studied.The PSF matrix is derived from the single photon incidence response function.A statistical iterative reconstruction(IR)method based on the system matrix containing the PSF is developed.More specifically,the gamma photon incidence upon a crystal array is simulated by Monte Carlo(MC)simulation,and then the single photon incidence response functions are calculated.Subsequently,the single photon incidence response functions are used to compute the coincidence blurring factor according to the physical process of PET coincidence detection.Through weighting the ordinary system matrix response by the coincidence blurring factors,the IR system matrix containing the PSF is finally established.By using this system matrix,the image is reconstructed by an ordered subset expectation maximization(OSEM)algorithm.The experimental results show that the proposed system matrix can substantially improve the image radial resolution,contrast,and noise property.Furthermore,the simulated single gamma-ray incidence response function depends only on the crystal configuration,so the method could be extended to any PET scanner with the same detector crystal configuration. 相似文献
993.
Pre-treatment process is the key step for electroless plating. Once a suitable pre-treatment film is in place, the desired metals can be plated. In this paper, Ni-P coating was successfully prepared on AZ33 magnesium alloy with Mg(OH)2 pre-treatment film by electroless plating. To investigate the role of MgF2 in Ni-P coating, the deposition procedures between Mg(OH)2 pre-treatment film and Mg(OH)2-MgF2 pre-treatment film (a traditional process) were compared. The surface morphology variations of coatings were observed with scanning electron microscopy and the compositions were analyzed by energy dispersive spectrometry. The results showed that during the plating, both MgF2 and Ni-P deposited at the initial stage, and MgF2 distributed in the bottom of the coating, forming a transitional interlayer with Ni- P. According to the heat quench test, a poor adhesion of the coating mainly occurred between the MgF2 and Ni-P coating. 相似文献
994.
Xue Li Guangyue Hou Junpeng Xing Fengrui Song Zhiqiang Liu Shuying Liu 《Journal of the American Society for Mass Spectrometry》2014,25(12):2181-2184
In the present work, direct analysis of real time ionization combined with multi-stage tandem mass spectrometry (DART-MSn) was used to investigate the metabolic profile of aconite alkaloids in rat intestinal bacteria. A total of 36 metabolites from three aconite alkaloids were identified by using DART-MSn, and the feasibility of quantitative analysis of these analytes was examined. Key parameters of the DART ion source, such as helium gas temperature and pressure, the source-to-MS distance, and the speed of the autosampler, were optimized to achieve high sensitivity, enhance reproducibility, and reduce the occurrence of fragmentation. The instrument analysis time for one sample can be less than 10 s for this method. Compared with ESI-MS and UPLC-MS, the DART-MS is more efficient for directly detecting metabolic samples, and has the advantage of being a simple, high-speed, high-throughput method. Graphical Abstract
? 相似文献
995.
Hui-Ling Feng Ling Tian Wei-Ming Chai Xiao-Xin Chen Yan Shi Yu-Sen Gao Chong-Ling Yan Qing-Xi Chen 《Applied biochemistry and biotechnology》2014,173(1):179-192
Flamboyant tree, a kind of medicinal plant, was studied as a source of condensed tannins. The antioxidant activities of the condensed tannins from the leaf, fruit, and stem bark of flamboyant tree were screened by ABTS radical and hydroxyl radical scavenging activity methods. The results indicated that these compounds possessed potent antioxidant activity. Their structures were then characterized by high-performance liquid chromatography-electrospray ionization mass spectrometry (HPLC-ESI-MS) after thiolytic degradation. The results showed that the leaf condensed tannins were composed of afzelechin/epiafzelechin, catechin/epicatechin, and gallocatechin/epigallocatechin, while the fruit and stem bark condensed tannins had afzelechin/epiafzelechin and catechin/epicatechin. In addition, the condensed tannins were evaluated for their antityrosinase ability. They were found to have significant antityrosinase activity. The IC50 values were 35 ± 2.0 and 40 ± 0.5 μg/ml for the condensed tannins of fruit and stem bark, respectively. Further, fluorescence quenching and copper interacting techniques were utilized to unravel the molecular mechanisms of the inhibition. The results showed that the hydroxyl group of the condensed tannins could chelate the dicopper center of the enzyme and interact with tryptophan residues. Our studies revealed that condensed tannins might be suitable for use in food, agriculture, cosmetic, nutraceutical, and pharmaceutical applications. 相似文献
996.
Chengliang Xiao Anyun Zhang Zhifang Chai 《Journal of Radioanalytical and Nuclear Chemistry》2014,299(1):699-708
To separate Cs(I) from highly active liquid waste, a macroporous silica-based 25, 27-bis(iso-propyloxy)calix[4]arene-26,28-crown-6 (BiPCalix[4]C6) supramolecular recognition material, BiPCalix[4]C6/SiO2–P, was synthesized and characterized by SEM, FT-IR, and TG-DSC. The adsorption properties of BiPCalix[4]C6/SiO2–P and a macroporous polymer-based supramolecular recognition composite, BiPCalix[4]C6/XAD-7, were compared. It was found that BiPCalix[4]C6/SiO2–P exhibited better adsorption ability and faster adsorption dynamics than BiPCalix[4]C6/XAD-7. The adsorption isotherm of Cs(I) onto BiPCalix[4]C6/SiO2–P was studied at 298 K and it was well described by Langmuir isotherm model. The complex composition between BiPCalix[4]C6/SiO2–P and Cs(I) was determined as 1:1 type by investigating the effect of the concentrations of BiPCalix[4]C6, Cs(I), and H+ on the adsorption. Meanwhile, the selectivity of BiPCalix[4]C6/SiO2–P towards Na(I), K(I), Rb(I), Cs(I), Sr(II), Ba(II), Ru(III), Mo(VI), La(III), and Y(III) was investigated. 相似文献
997.
Kian Hoong Chai Loong Kong Leong David Shan-Hill Wong De-Hao Tsai Sumathi Sethupathi 《中国化学会会志》2020,67(6):998-1008
The present work studied the effect of different carbon dioxide (CO2) adsorbents on Ni-based dual-function materials (DFMs) for the development of carbon capture and on-site utilization in a reactor at isothermal condition. The DFMs containing Ni functioning as a methanation catalyst with various CO2 adsorbents (i.e., CaO, MgO, K2CO3, or Na2CO3) were prepared on γ-Al2O3 through sequential impregnation. The result indicated that Ni-Na2CO3/γ-Al2O3 had the highest methanation capacity (i.e., 0.1783 mmol/g) and efficiency (i.e., 71.09%) in the CO2 adsorption–methanation test. The CO2 uptake and the subsequent methanation capacity of the Ni-Na2CO3/γ-Al2O3 increased to more than 24 times and more than 17 times, respectively, compared to Ni/γ-Al2O3. The high methanation capacity was correlated to its highest amount of weak basic sites, substantial CO2 capture capacity and capture/release efficiency, and reactivity to H2 at a lower temperature, supported by CO2-TPD, TGA analyses for adsorption or adsorption–desorption at the isothermal condition, and H2-TPRea, respectively. A continuous cyclic CO2 adsorption–methanation was performed by using the Ni-Na2CO3/γ-Al2O3 and Ni-CaO/γ-Al2O3, showing that the CO2 adsorption capacity was stabilized from third cycle onward, whereas the methanation capacity was stabilized at all cycles, indicating the high stability of the DFMs for both CO2 adsorption and subsequent methanation. This work demonstrated successful synthesis of the Ni-based, low-cost, and stable DFMs with the ability to produce methane via the direct capture of CO2. 相似文献
998.
Based on target recycling amplification, the development of a new label-free, simple and sensitive colorimetric detection method for ATP by using un-modified aptamers and DNAzymes is described. The association of the model target molecules (ATP) with the corresponding aptamers of the dsDNA probes leads to the release of the G-quadruplex sequences. The ATP-bound aptamers can be further degraded by Exonuclease III to release ATP, which can again bind the aptamers of the dsDNA probes to initiate the target recycling amplification process. Due to this target recycling amplification, the amount of the released G-quadruplex sequences is significantly enhanced. Subsequently, these G-quadruplex sequences bind hemin to form numerous peroxidase mimicking DNAzymes, which cause substantially intensified color change of the probe solution for highly sensitive colorimetric detection of ATP down to the sub-nanomolar (0.33 nM) level. Our method is highly selective toward ATP against other control molecules and can be performed in one single homogeneous solution, which makes our sensing approach hold great potential for sensitive colorimetric detection of other small molecules and proteins. 相似文献
999.
We report on a novel electrochemical signal amplification strategy for use in immunoassays. The highly responsive immunoelectrode was constructed in the following way: (1) The surface of a gold electrode was covered with a layer single-walled carbon nanotubes dispersed in chitosane functionalized with L-cysteine; (2) Gold nanoparticles containing protein A and anti-alpha-fetoprotein (anti-AFP) were then covalently attached to the surface via the thiol groups of the chitosane. The electrode is then exposed to the analyte (AFP) which then is bound by the antibody. In the next step, a gold-conjugated secondary antibody is added that was prepared in the following way: (1) Horseradish peroxidase was crosslinked and the resulting spheres were coated with hollow gold nanoparticles (hollow Au-NPs) to give nanospheres of ~100 nm in diameter. (2) These were the coated with thionine and, in a last step, with secondary antibody. The use of these materials has several attractive features: The HRP-NPs functionalized with hollow Au-NPs possess a large surface area that can load the large amount of secondary antibody. Thionine (Thi) is highly redox active and improves the intensity of the signal. Carbon nanotubes were used because they possess an excellent electron transfer rate and large surface area. Following incubation of the modified electrode (a) with a sample containing AFP, (b) then with the secondary antibody, and (c) with washing buffer, the electrode is placed in a solution containing H2O2. The HRP in the smart secondary antibody causes the catalytic decomposition of H2O2 and the results in an electrical current that is linearly related to the concentration of AFP in the 0.025 to 5.0 ng mL?1 concentration range. The detection limit for AFP is as low as 8.3 pg mL?1. We believe that this novel kind of immunoassay represents a promising tool for use in sensitive clinical assays. Graphical Abstract
A novel signal amplification strategy was presented, which is based on the attachment of hollow gold nanoparticles on the surface of immobilized horseradish peroxidase nanospheres. Its application to immunoassay displayed a wide linear response range with low detection limit. 相似文献
1000.
Filling Carbon Nanotubes with Prussian Blue Nanoparticles of High Peroxidase‐Like Catalytic Activity for Colorimetric Chemo‐ and Biosensing
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Ting Wang Dr. Yingchun Fu Prof. Liyuan Chai Long Chao Lijuan Bu Yue Meng Dr. Chao Chen Prof. Ming Ma Prof. Qingji Xie Prof. Shouzhuo Yao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(9):2623-2630
Facile filling of multiwalled carbon nanotubes (MWCNTs) with Prussian blue nanoparticles (PBNPs) of high peroxidase‐like catalytic activity was performed to develop novel colorimetric sensing protocols for assaying H2O2 and glucose. Fine control of PBNP growth was achieved by modulating the concentration ratio of K3[Fe(CN)6] and FeSO4 precursors in an acidic solution containing ultrasonically dispersed MWCNTs, and thus size‐matched PBNPs could be robustly immobilized in the cavities of the MWCNTs (MWCNT‐PBin). Unlike other reported methods involving complicated procedures and rigorous preparation/separation conditions, this mild one‐pot filling method has advantages of easy isolation of final products by centrifugation, good retention of the pristine outer surface of the MWCNT shell, and satisfactory filling yield of (24±2) %. In particular, encapsulation of PBNPs of poor dispersibility and limited functionality in dispersible and multifunctional MWCNT shells creates new and valuable opportunities for quasihomogeneous‐phase applications of PB in liquid solutions. The MWCNT‐PBin nanocomposites were exploited as a peroxidase mimic for the colorimetric assay of H2O2 in solution by using 3,3′,5,5′‐tetramethylbenzidine (TMB) as reporter, and they gave a linear absorbance response from 1 μM to 1.5 mM with a limit of detection (LOD) of 100 nM . Moreover, glucose oxidase (GOx) was anchored on the outer surface of MWCNT‐PBin to form GOx/MWCNT‐PBin bionanocomposites. The cooperation of outer‐surface biocatalysis with peroxidase‐like catalysis of interior PB resulted in a novel cooperative colorimetric biosensing mode for glucose assay. The use of GOx/MWCNT‐PBin for colorimetric biosensing of glucose gave a linear absorbance response from 1 μM to 1.0 mM and an LOD of 200 nM . The presented protocols may be extended to other multifunctional nanocomposite systems for broad applications in catalysis and biotechnology. 相似文献